1. Field of the Invention
This invention relates to a combustion chamber for a gas turbine engine and more particularly to a doublewall combustion chamber configuration providing a flow path for convectively cooling the combustion chamber wall.
2. Description of the Prior Art
Cylindrical, step-liner combustion chambers for gas turbines are well known. In such combustion chambers the step-liner configuration defines cylindrical segments extending axially with each downstream segment having a slightly larger diameter than the immediately preceding segment of the combustion chamber and generally with the leading edge of the larger diameter downstream segment overlapping the terminal edge of the upstream segment to define an annular, axially extending airflow path between adjacent segments. The adjacent segments are supported in such configuration by support means extending generally radially between the overlapping portions thereof permitting an entry for cooling air, flowing exteriorly of the combustion chamber, to enter the chamber through the annular passage. Such cooling air, while flowing over the outer surface of the upstream segments, tends to cool the upstream segment by convectively removing the heat therefrom, and, upon entering the annular passage, continues to flow along the inside surface of the downstream segment to form a layer of barrier or film cooling air, protecting the inner surface of the combustion chamber from the combustion gases therewithin. Thus, it is apparent that the cooling provided the downstream segment by such air is not as dependent upon the air having a low temperature as it is upon the air maintaining a protective layer.
In order to increase the effective convective cooling provided by the otherwise randomly circulating air on the exterior surface of the upstream segment, it is desirable to direct the air in close proximity and at relatively high velocity adjacent the exterior surface. Preferably, a certain amount of turbulence will also be established in this cooling air to maximize the cooling effect of the flowing air.
Heretofore, a double-wall step-liner combustion chamber was provided, such as shown in U.S. Pat. No. 3,702,058 having a common assignee as the present invention, wherein an outer annular sleeve or baffle encircled each cylindrical segment of the chamber and was maintained in annular-spaced relation thereabout by an annular corrugated member or wiggle strip, with all components being assembled and welded together to provide an integral structure. However, the variations and gradations in temperatures between the various components (the combustion chamber wall being substantially hotter, and on the order of about 1400.degree. F., than the outer wall, which may be on the order of about 750.degree. F.), resulted in relative thermal expansion therebetween, both axially and radially which, in turn, developed areas of high stress in the respective parts leading to, over and extended period of time, failures thereof.